Many lighting systems use lamps which are powered by electronic or magnetic inductive devices, e.g., ballasts, that control the applied voltage and current. Conventional ballasts often use “open core and coil” construction, in which a core of laminated steel, iron, or similar material has windings of exposed coils of wire. Transformers can also be constructed in this open core and coil format.
It is well known that lighting systems consume energy which is converted into usable light and a typically undesirable amount of heat. Heat can be very damaging to lighting components, causing compromised performance or failure. Leaving burned-out lamps in the fixture, using the wrong size lamps, incorrect wiring, incorrect line voltage, component failure, operation at temperatures below or above the rated limits or power surges can all cause a ballast to overheat and fail. A failing ballast can get extremely hot and become a fire hazard. While some ballasts include a safety device which shuts the ballast off in case of extreme thermal conditions, certain types of failure may prevent that shutdown. Therefore, a medium for dissipating heat is critical to the performance of ballasts.
The mounting of core and coil ballasts within the enclosure of a lighting fixture housing is critical to its operation. While heat dissipation leading to premature ballast failure can be prevented by using an open core and coil ballast (rather than an encapsulated ballast), it is typically necessary to install the open core and coil ballast in a way that conduction and radiation take place to dissipate the heat generated.
Typically, heat is transferred from the ballast to the fixture housing which encloses the ballast, lamp and other electrical lighting fixtures. This heat transfer may be facilitated by the application of grease, gel, resin and the like to the single surface of the ballast case which is connected with respect to the housing. Mounting plates have also been used to provide a medium for heat transfer from one surface of the ballast to one surface of the housing. While heat transfer is a major concern in housing design, the housing must also provide free access to ballast components and wiring so that maintenance can be performed.
In addition, many users of lighting fixtures require that the dimensions of the fixtures be made as small as possible so that the fixtures utilize as little of the space of an installation site as possible. For outdoor floodlighting, it is important that the fixtures be as unobtrusive as possible and capable of blending in with the surrounding architecture or of being hidden. For industrial-type lighting fixtures for low and medium height mounting installations, it is important that the fixtures interfere as little as possible with existing equipment such as air-conditioning and heating equipment, fire sprinkler systems and plumbing and electrical equipment. Whatever their use, it is desirable that the fixtures minimize material costs, comprise as few parts as possible and be easily and quickly assembled to minimize manufacturing costs.
Typical housings for electrical lighting fixtures are constructed from aluminum, steel, composites or other metals and must be designed in view of these size concerns as well as a variety of factors including separation of the ballast from other heat-sensitive components, aesthetic appeal, and the ability to transfer heat, among others. In the prior art, these concerns have resulted in housings which provide for heat transfer from the ballast to the housing only through brackets or mounting plates or from one surface of the ballast to only one surface of the housing. Such prior art housings and ballasts do not provide sufficient heat transfer for certain applications.
Therefore, there is a need for an improved housing for electrical lighting fixtures which provides for increased heat transfer from ballasts. There is also a need for a compact, low-cost, reliably assembled, and easily usable housing for electrical lighting fixtures which ensures good thermal transfer from a ballast enclosed therein.